• The Moon has water at places where none had been detected before, and has potentially more water than previously believed in regions where it was already understood to exist. In two separate studies in Nature Astronomy, scientists have reported findings with potentially huge implications for sustaining humans on the Moon in the future. One study reports the detection of water on the Moon’s sunlit surface for the first time. The other estimates that the Moon’s dark, shadowy regions, which potentially contain ice, are more widespread than thought.

Why is the discovery of water important?

  • Apart from being a marker of potential life, water is a precious resource in deep space. For astronauts landing on the Moon, water is necessary not only to sustain life but also for purposes such as generating rocket fuel. NASA’s Artemis programme plans to send the first woman and the next man to the Moon in 2024, and hopes to establish a “sustainable human presence” there by the end of the decade. If space explorers can use the Moon’s resources, it means they need to carry less water from Earth.

What was known about water on the Moon?

  • Previous Moon studies, including by the Indian Space Research Organisation’s (ISRO) Chandrayaan-1 mission, have provided evidence for the existence of water. In 2009, the Moon Mineralogy Mapper (M3) instrument aboard Chandrayaan-1 found water molecules in the polar regions. A paper in Nature Geoscience In August 2013 analysed M3 data to report the detection of magmatic water (water originating from the deep interiors) on the Moon’s surface.
  • However, what was not established in such studies — based on observations by the Chandrayaan-1 mission, NASA’s Cassini and Deep Impact comet mission, and NASA’s ground-based Infrared Telescope Facility — was whether the detected molecules were water as we know it (H20) or in the form of hydroxyl (OH).

What is different in the new discovery?

  • This time, it is confirmed H20 molecules, discovered in Clavius Crater in the Moon’s southern hemisphere. And it is the first time water has been detected on the sunlit side, showing it is not restricted to the shadowy regions.
  • SOFIA, which is a modified Boeing 747SP jetliner that flies at altitudes up to 45,000 feet, has an infrared camera that picked up the wavelength unique to water molecules. The data showed water in concentrations of 100-412 parts per million trapped in 1 cubic metre of soil.
  • SOFIA’s mission is to look at dark and distant objects. The Moon, on the other hand, is so close and bright that it fills the SOFIA guide camera’s entire field of view. In August 2018, just to check whether SOFIA could reliably track the Moon, scientists tried a test observation. It was from this test that came the detection of water. Scientists are now planning more observational flights.

How could the water have formed?

  • Space rocks carrying small amounts of water could have bombarded the Moon. Alternatively, the Sun’s solar wind could have carried hydrogen, which then reacted with minerals in the lunar soil to create hydroxyl, which later transformed into water.
  • The sunlit surface retaining the water presents a puzzle, since the Moon does not have a thick atmosphere. One possibility is that the water gets trapped into tiny bead-like structures that were created in the soil by impacts from space rocks. Alternatively, the water could be hidden between grains of lunar soil and sheltered from the sunlight, NASA said.

So, how widespread is water on the Moon?

  • On the sunlit side, it is not yet known whether the water SOFIA found is easily accessible. On the other hand, the hidden, shadowy pockets on the lunar surface called “cold traps” are spread across a combined 40,000 sq km, the other study has reported. That is roughly the size of Kerala.
  • The estimate used mathematical tools to analyse data from NASA’s Lunar Reconnaissance Orbiter. The cold traps have gone without sunlight for potentially billions of years. If they do contain ice, it means water is going to be more accessible than previously assumed.

What next?

  • SOFIA will look for water in additional sunlit locations to learn more about how the water is produced, stored, and moved across the Moon. Meanwhile, NASA’s Volatiles Investigating Polar Exploration Rover (VIPER) will carry out a mission to create the first water resource maps of the Moon.